io_uring: add support for IORING_OP_ACCEPT

This allows an application to call accept4() in an async fashion. Like
other opcodes, we first try a non-blocking accept, then punt to async
context if we have to.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -1686,6 +1686,40 @@ static int io_recvmsg(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 #endif
 }
 
+static int io_accept(struct io_kiocb *req, const struct io_uring_sqe *sqe,
+		     struct io_kiocb **nxt, bool force_nonblock)
+{
+#if defined(CONFIG_NET)
+	struct sockaddr __user *addr;
+	int __user *addr_len;
+	unsigned file_flags;
+	int flags, ret;
+
+	if (unlikely(req->ctx->flags & (IORING_SETUP_IOPOLL|IORING_SETUP_SQPOLL)))
+		return -EINVAL;
+	if (sqe->ioprio || sqe->off || sqe->len || sqe->buf_index)
+		return -EINVAL;
+
+	addr = (struct sockaddr __user *) (unsigned long) READ_ONCE(sqe->addr);
+	addr_len = (int __user *) (unsigned long) READ_ONCE(sqe->addr2);
+	flags = READ_ONCE(sqe->accept_flags);
+	file_flags = force_nonblock ? O_NONBLOCK : 0;
+
+	ret = __sys_accept4_file(req->file, file_flags, addr, addr_len, flags);
+	if (ret == -EAGAIN && force_nonblock) {
+		req->work.flags |= IO_WQ_WORK_NEEDS_FILES;
+		return -EAGAIN;
+	}
+	if (ret < 0 && (req->flags & REQ_F_LINK))
+		req->flags |= REQ_F_FAIL_LINK;
+	io_cqring_add_event(req->ctx, sqe->user_data, ret);
+	io_put_req(req, nxt);
+	return 0;
+#else
+	return -EOPNOTSUPP;
+#endif
+}
+
 static void io_poll_remove_one(struct io_kiocb *req)
 {
 	struct io_poll_iocb *poll = &req->poll;
@@ -2173,6 +2207,9 @@ static int __io_submit_sqe(struct io_ring_ctx *ctx, struct io_kiocb *req,
 	case IORING_OP_TIMEOUT_REMOVE:
 		ret = io_timeout_remove(req, s->sqe);
 		break;
+	case IORING_OP_ACCEPT:
+		ret = io_accept(req, s->sqe, nxt, force_nonblock);
+		break;
 	default:
 		ret = -EINVAL;
 		break;

include/uapi/linux/io_uring.h

@@ -19,7 +19,10 @@ struct io_uring_sqe {
 	__u8	flags;		/* IOSQE_ flags */
 	__u16	ioprio;		/* ioprio for the request */
 	__s32	fd;		/* file descriptor to do IO on */
-	__u64	off;		/* offset into file */
+	union {
+		__u64	off;	/* offset into file */
+		__u64	addr2;
+	};
 	__u64	addr;		/* pointer to buffer or iovecs */
 	__u32	len;		/* buffer size or number of iovecs */
 	union {
@@ -29,6 +32,7 @@ struct io_uring_sqe {
 		__u32		sync_range_flags;
 		__u32		msg_flags;
 		__u32		timeout_flags;
+		__u32		accept_flags;
 	};
 	__u64	user_data;	/* data to be passed back at completion time */
 	union {
@@ -65,6 +69,7 @@ struct io_uring_sqe {
 #define IORING_OP_RECVMSG	10
 #define IORING_OP_TIMEOUT	11
 #define IORING_OP_TIMEOUT_REMOVE	12
+#define IORING_OP_ACCEPT	13
 
 /*
  * sqe->fsync_flags